Optics Question 630
Question: A thin lens made of glass of refractive index 1.5 has a front surface + 11 D power and back surface - 6 D. If this lens is submerged in a liquid of refractive index 1.6, the resulting power of the lens is
[SCRA 1994]
Options:
A) -0.5 D
B) + 0.5 D
C) - 0.625 D
D) + 0.625 D
Show Answer
Answer:
Correct Answer: C
Solution:
Total power $ P=P _{1}+P _{2}=11-6=5D $
Also $ \frac{f _{l}}{f _{a}}=\frac{{( _{a}}{\mu _{g}}-1)}{{( _{l}}{\mu _{g}}-1)}\Rightarrow \frac{P _{a}}{P _{l}}=\frac{{( _{a}}{\mu _{g}}-1)}{{( _{l}}{\mu _{g}}-1)} $
$ \Rightarrow $ $ \frac{5}{P _{l}}=\frac{(1.5-1)}{(1.5/1.6-1)}\Rightarrow P _{l}=-0.625D $
